TECH 1
How to increase HORSEPOWER!
I think we all can agree that when it comes to increasing useable horsepower, four areas that can
help achieve this are increasing the engine's mechanical efficiency(ME), thermal efficiency(TE),
volumetric efficiency(VE) and combustion efficiency(CE). Let's take a look.

Engineers refer to
powertrain drag as “parasitic drag”.  It seems to fit.  It’s almost like a parasite
leaching power away from any component with closely fitted parts. This "parasitic drag"
decreases  the
mechanical efficiency(ME) of an engine through frictional, inertial and pumping
losses.

The (ME) is a ratio of the "power produced" to the "power doing work". Engine parts, especially
main and rod bearings, pistons and valve train components, are subject to high frictional losses
and can account for about 10% of total engine heat and up to 10% of the total power loss. The
higher the engine operating rpm, the higher the frictional losses.

Engine accessories such as water pump, power-steering pump, alternator and clutches all have to
overcome friction to operate and place more load on the engine.
Inertial drag is closely related to
frictional drag in this instance. Reducing inertial drag, (less rotating mass) which increases the
(ME),  can also affect frictional drag. Installing lighter pistons, a lighter flywheel or by installing
underdrive accessory pulleys are ways of reducing inertial drag. Even more
horsepower in an
engine can be gained by reducing frictional losses and increasing it's (ME). A 20% reduction in
friction pressure will yield approximately a 5% increase in efficiency.

Reducing frictional drag first involves
metal separation. If metal separation can be achieved, not
only can heat and friction be greatly reduced, but metal wear and metal transfer can also be
greatly reduced too. This can extend component longevity as well.

Lubricant film strength is determined by its ability to separate metal under stress. The higher the
stress the higher the lubricant film strength needed for metal separation. Lubricant film strength
specifications are partially determined by viscosity, and partly determined by the lubricity
(slipperiness) of the additive package.

Viscosity, or oil thickness, characterizes its fluidity, or its flow ability. The viscosity can be
expressed as "millimeters squared per second" (mm^2/s). A higher viscosity oil increases
viscous
friction
, or oil drag, but usually has a higher film strength. Viscosity specifications are usually
determined by the oil clearances of the application. Larger oil clearances have a thicker layer of
oil for maximum metal separation (hydrodynamics), but the increase in oil drag decreases (ME).

Smaller oil clearances are a growing trend, especially in smaller displacement, high rpm engines.
In order to increase (ME), a significantly thinner layer of oil is needed with a higher risk of metal
transfer and wear.
Thin film strength becomes critical at this point, and this is where the lubricity
plays more of a role in metal separation since thinner viscosity oils are often employed. Not only
does the thin layer of oil have to endure more heat from the tighter clearances, it has to have high
thin film strength and be able to cling to and work into the pores of the metal for complete metal
separation and less oil drag. This means more(ME) and more
usable horsepower!  

Frictional drag and oil drag can also be reduced in the
drivetrain for optimum efficiency. Frictional
losses in the drivetrain can be as much as 15% of the total power loss, depending on the
application.  Manual gearboxes, transfer cases, rear gears/ differentials and power steering
pumps are all areas where an increase in efficiency can mean more power.  


The second way we can increase
horsepower is by increasing cylinder pressure. This means
increasing cylinder combustion temperatures without going too "hot" and causing  pre-ignition or
detonation. This is usually achieved three separate ways, all essentially producing the same
results,
without having to increase bore/stroke.
They are:

 1. Increasing cylinder A/F volumetric efficiency(VE)
           
 2. Increasing compression ratio or thermal efficiency(TE)

 3. Optimizing the ignition timing points and spark intensity

Increasing the thermal efficiency(TE) of an engine means more heat can be converted to
mechanical energy at the piston. The (TE) is a ratio of "heat produced" to "heat that produces
work". Typically less than 33% of the combustion heat is producing work. The heat losses are
mostly due to heat absorbtion from the cooling system and from the exhaust gases. Increasing the
compression ratio(CR) is a common way to increase (TE). Special metal coatings are sometimes
employed to reflect heat, rather than absorb it to help minimize
total heat losses.

Optimizing the ignition timing points and increasing the spark kernel intensity can increase peak
cylinder pressures and can increase the  combustion flame speed, or the burn rate of the fuel.
This can help increase
combustion efficiency(CE), which is a ratio of "total fuel burnt" to "total fuel
that was available to burn".  If more fuel could be burned, then more heat can be produced to
perform work on the piston. More of this subject is covered in another tech page on racing fuels.

We will be looking mostly at option one
volumetric efficiency(VE), which is a ratio of  "total air-fuel
mass in a cylinder" to "total air-fuel mass that a cylinder can hold".  Increasing (VE) means
charging a cylinder with a denser
air-fuel(AF) mass. In theory an engine is operating at 100%
[(VE)=100%] at wide open throttle operation, when the intake manifold is fully pressurized.

At part throttle [(VE)<100%] the intake manifold has more vacuum, which reduces the (AF) mass
charging the cylinders. The more vacuum present in the manifold, the more cylinder pumping and
(AF) mass losses. Pumping losses decrease the overall (ME) of an engine because the pistons
work harder to draw in an (AF) mass.

Whenever [(VE)>100%] ,  the (TE) will increase because the (AF) mass is denser and will
increase compression pressures and temperatures. This will increase (CE) as the higher
pressures and temperatures will increase flame speed and completeness of burn.

Because air is made up of only 21% oxygen, even in an unrestricted naturally aspirated engine, it
is difficult to achieve 100% volumetric efficiency during wide open throttle cylinder charging with
only 14.7 psi (atmospheric air pressure) behind it.  
Three ways to increase (VE) are:


 1. Forced induction (supercharger / turbocharger)

 2. Nitrous oxide injection

 3. Chemical oxygenating agents


Superchargers and turbochargers are probably the most popular ways to increase cylinder
pressure and (VE).  Air pressure can be increased or boosted several psi to increase oxygen
content during cylinder charging. These systems are usually very expensive, require engine
compartment reconfiguration and specific ignition timing and fuel ratio tuning maps. Intake charge
cooling (charge air cooling) is also usually required as the compressed air is hotter.

Nitrous oxide injection is another popular way to increase cylinder pressure and (VE) by injecting
nitrous oxide and extra fuel into the air induction system. This can charge a cylinder  to well over
100% efficiency depending on amount injected. It also provides thermal-charging by cooling the
incoming air. These systems are moderately priced, requires little engine compartment
reconfiguration, allows adjustable cylinder charge rates and (if used in small enough amounts)
usually requires no tuning. Nitrous bottles have to be refilled though.

Chemical oxygenating agents or "chemical supechargers" is another way to increase cylinder
pressure and (VE) by releasing oxygen in the cylinders during combustion through the fuel
induction system. This can also charge a cylinder to well over 100% efficiency depending on what
ratio the product is mixed with fuel. This also increases flame speed and (CE) because of the
oxygen content in the fuel, reducing the need for as much (AF) mixing. There is no system to
install and requires no engine compartment reconfiguration. It allows you to adjust cylinder charge
rates and can be used in small enough amounts to require no tuning.  The product needs to be
replaced like fuel.

Restoring lost horsepower:

Fuel and oil deposits in an engine (mostly on street operated vehicles) affect power and
performance mostly in three ways:

 1. Decreases A/F mass during cylinder charging (VE)

 2. Reduces cylinder compression pressures (TE)

 3. Reduces fuel efficiency (CE)

Carbon fuel deposits on intake valves can restrict measurable air and fuel flow (cfm) per cylinder
depending on the amount of build up. They can also affect proper valve closing resulting in
compression loss. Deposits on piston tops can interfere with piston cooling and cause detonation
or pre-ignition. Varnish/sludge/carbon deposits on oil control rings or compression rings can
result in additional cylinder compression loss and cylinder wall/ring wear.
Regular cleaning in these two areas are recommended for proper air/fuel ratio and maximum
cylinder compression.

                                                      
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